21356666520 has 512 divisors, whose sum is σ = 80024371200. Its totient is φ = 4451328000.

The previous prime is 21356666503. The next prime is 21356666521. The reversal of 21356666520 is 2566665312.

It is a super-2 number, since 2×21356666520² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (42).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21356666521) by changing a digit.

It is a polite number, since it can be written in 127 ways as a sum of consecutive naturals, for example, 53258320 + ... + 53258720.

It is an arithmetic number, because the mean of its divisors is an integer number (156297600).

Almost surely, 2^21356666520 is an apocalyptic number.

21356666520 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21356666520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40012185600).

21356666520 is an abundant number, since it is smaller than the sum of its proper divisors (58667704680).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21356666520 is a wasteful number, since it uses less digits than its factorization.

21356666520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 559 (or 555 counting only the distinct ones).

The product of its (nonzero) digits is 388800, while the sum is 42.

The spelling of 21356666520 in words is "twenty-one billion, three hundred fifty-six million, six hundred sixty-six thousand, five hundred twenty".